The work described herein consists of an examination of the effect of estrogen on the expression of the serum albumin gene in rooster liver. It has been demonstrated that the relative concentration of serum albumin mRNA in the liver decreased by approximately 50% following treatment with hormone. This decrease, however, does not stem from reduced expression of the gene but results from dilution of albumin mRNA with other stable and abundant mRNA species that increase markedly in concentration following the administration of estradiol. Albumin mRNA has been purified from rooster liver RNA to approximately 70% homogeneity by chromatography on diazotized cellulose to which a cloned albumin cDNA fragment had been attached. A procedure is being developed for specifically labeling the 5' terminus of any capped eukaryotic mRNA. It involves chemical removal of the cap structure followed by the reintroduction of 32P labeled GMP using the enzyme guanylyl transferase. RNA species labeled in this fashion will be used to select cloned genomic DNA fragments that contain the transcriptional initiation sites of several genes that are expressed at high levels in chicken liver.